Micromechanical components have been manufactured using the following steps: providing a substrate; providing a first micromechanical functional layer on the substrate; structuring the first micromechanical functional layer in such a manner that it has a sensor structure to be made movable; providing and structuring a first sealing layer on the structured first micromechanical functional layer; providing and structuring a second micromechanical functional layer on the first sealing layer, the second micromechanical functional layer having at least one sealing function and anchored at least partially in the first micromechanical functional layer; making the sensor structure movable; and providing a second sealing layer on the second micromechanical functional layer. German Published Patent Application No. 100 17 422.1 discusses a method of manufacturing a micromechanical component and a micromechanical component made by the method.
Monolithically integrated inertial sensors manufactured by surface micromechanics (SMM), in which the sensitive movable structures are situated on the chip without protection (analog devices) are conventional. This may result in increased expenses for handling and packaging.
This problem may be circumvented by a sensor in which the structures manufactured by surface micromechanics are covered by a second cap wafer. This type of packaging is responsible for a large share (approximately 75%) of the cost of an SMM acceleration sensor. These costs may arise as a result of the large sealing surface area that may be required between the cap wafer and the sensor wafer and are due to the complex structuring (2–3 masks, bulk micromechanics) of the cap wafer.
The structure of a function layer system and a method for hermetic capping of sensors using surface micromechanics is discussed in German Patent Application No. 195 37 814. The manufacture of the sensor structure using conventional technological methods is discussed. The cited hermetic capping is performed using a separate cap wafer made of silicon, which is structured using expensive structuring processes such as KOH etching. The cap wafer is applied to the substrate together with the sensor (sensor wafer) using a seal glass. This may require a wide bonding frame around each sensor chip to ensure an adequate adhesion and sealing ability of the cap. This may limit the number of sensor chips per sensor wafer considerably. Due to the large amount of space which may be required and the expensive manufacture of the cap wafer, sensor capping may incur considerable costs.
German Published Patent Application No. 100 17 422.1 relates to a manufacturing method and component based on a conventional SMM process, and discusses creating epitaxial polysilicon having a thickness of at least 10 μm to form a micromechanical functional layer. No new permeable layer may be required, but conventional processes may be used.
The SMM process is simplified, because the cap wafer may no longer be required and the structures can be bonded from the top due to the second micromechanical functional layer, which assumes at least one sealing function.
Furthermore, the functionality of the process is enhanced, i.e., additional mechanical and/or electrical components are available to the designer for implementing the component. In particular, the following function elements may be produced:                a pressure sensor membrane in the second micromechanical functional layer;        a printed circuit structure in the second micromechanical functional layer, which may intersect an additional printed circuit structure provided above the second sealing layer;        low-resistance aluminum leads in the top of the additional printed conductor structure provided in the second sealing layer;        a vertical differential capacitor; and        additional anchor points of the structures of the first micromechanical functional layer in the second micromechanical functional layer.        
Conventional IC (Integrated Circuit) packaging methods such as hybrid, plastic, flip-chip, etc., may also be used.
FIG. 6 shows a detail V of a micromechanical component for elucidating the disadvantages sought to be overcome by the present invention.
In FIG. 6, reference number 1 identifies a silicon substrate wafer; 4 identifies a sacrificial oxide, 5 identifies a first micromechanical functional layer in the form of an epitaxial polysilicon layer, 6 identifies a sensor structure (comb structure) to be made subsequently movable by etching sacrificial layer 4 and layer 8, 7 identifies trenches in first micromechanical functional layer 5, 8 identifies a first sealing oxide (LTO, TEOS or the like), which may be a refill layer, 9 identifies plugs in trenches 7, composed of sealing oxide 8, and 10 identifies a second micromechanical functional layer in the form of an epitaxial polysilicon layer having a sealing function.
In the refill process for depositing layer 8, trenches 7 of sensor structure 6 to be made movable are filled, i.e., as shown, plugged at the top only, thus producing a planar surface, on which second micromechanical functional layer 10 having the sealing function is applied, for example, as epitaxial polysilicon. In particular in the case of sensor structures 6 having a high aspect ratio, which are produced from the above-mentioned surface micromechanical epitaxial polysilicon, it is very difficult to fill deep trenches 7. Therefore, as shown, only the wafer surface is covered and trenches 7 are only sealed, i.e., plugged using plugs 9, on the top.
This refill process is only capable of sealing trenches 7 up to a width of approximately 5 μm without much oxide being deposited on the bottom of trench 7. This maximum width A provides the maximum possible vibration amplitude of the respective movable sensor structure 6, which forms a rotational rate sensor, for example.
FIG. 7 shows a modification of the detail of FIG. 6 to elucidate the disadvantages sought to be overcome by the present invention.
If wider trenches 77 (having a width of 15 μm, for example) were to be sealed using the refill process described with reference to FIG. 6, maximum possible deflection A′ of a movable sensor structure 6 would be further limited, namely to the thickness of refill material 8 on the side wall of movable sensor structure 6 (after removal of refill material 8).
FIG. 8 shows another modification of the detail of FIG. 6 to elucidate the disadvantages sought to be overcome by the present invention.
FIG. 8 shows the deposition of refill material 8 on the surface not to scale for greater clarity.
In order to make maximum deflection A″ of movable sensor structure 6 of the same magnitude as wider trench 77, wider trench 77 may be completely filled with refill material 8 so that sealing polysilicon 10 will only be deposited above sensor structure 6. This may result in the following disadvantages of the process control:                a longer deposition process of refill material 8;        additional required planarization of refill material 8, because high steps are created and no accurate lithography, required for contact holes 22, for example, may be possible any longer; and        a long and more complex process for removing the refill material.        